Quaternary ammonium salts carrying two hydrophobic long chain hydrocarbon moieties have found broad use as fabric softener actives. Quaternary ammonium salts of alkanolamines esterified with on average two fatty acid moieties per molecule, commonly referred to as ester quats, have largely replaced earlier alkyl quaternary ammonium compounds because of their biodegradability.
Tris-(2-hydroxyethyl)-methylammonium methylsulfate fatty acid esters made by quaternizing fatty acid esters of triethanolamine with dimethylsulfate have found broad use as fabric softener actives. Since dimethylsulfate is a potential carcinogen, quaternizing is carried out to achieve complete conversion of dimethylsulfate and a high conversion of amine. It has now been found that tris-(2-hydroxyethyl)-methylammonium methylsulfate fatty acid esters made this way contain unexpectedly high amounts of methanol. Although tris-(2-hydroxyethyl)-methylammonium methylsulfate fatty acid ester softener actives have been in use for more than 20 years, the high content of methanol in these compositions has remained unnoticed.
Since methanol is toxic and presents a workplace hazard, there is therefore a need to provide fabric softener active compositions comprising tris-(2-hydroxyethyl)-methylammonium methylsulfate fatty acid esters which compositions have a low content of methanol. There is also a need for a simple method for making such compositions.
It has now been found that fabric softener active compositions comprising tris-(2-hydroxyethyl)-methylammonium methylsulfate fatty acid esters and having a low content of methanol can be made by quaternizing fatty acid esters of triethanolamine with dimethylsulfate in the presence of a solid acid scavenger.